The invention relates to a housing, which can be manufactured cost-effectively, for a motor or compressor, to a motor or compressor having said housing, and to a production method.
For the supply of compressed air to pneumatic brake systems of heavy goods vehicles and buses, use is generally made of compressors with one to two pistons. A crankshaft is set in rotation by means of a drive source. Connecting rods are rotatably mounted both on the crankshaft and on the pistons. The rotational movement of the crankshaft is converted by the connecting rods into an upward and downward movement of the pistons in their cylinders. The air is compressed by means of said upward and downward movement. The housings of such compressors are generally cast in one piece from cast iron in a sand mold or a permanent mold. As an alternative, it is known for grey cast-iron cylinders cast in one piece in a sand mold to be mounted onto a base housing composed of aluminum that has been produced by high-pressure casting.
In the case of compressors with two or more cylinders, the production of the large crank chamber in which the crankshaft moves during operation is very difficult using high-pressure casting methods. Therefore, that part of the housing which includes the crank chamber is commonly manufactured in two pieces. This necessitates a cumbersome assembly process after the casting, and creates connection points between the housing parts, which are in principle susceptible to leakage.
The problem addressed by the invention is therefore that of providing a housing for a motor or compressor, which housing is easier to manufacture in one piece, such that it is easier to assemble and is at the same time less susceptible to leakage than the housings manufactured from multiple pieces according to the prior art.
This problem is solved by a housing according to embodiments of the invention, as well as by a motor or compressor with said housing, and by a production method for the housing and motor.
In the context of the invention, a housing for a motor or compressor has been developed. The housing has an elongate crank chamber which has two end surfaces. “Elongate” is to be understood to mean that the crank chamber extends along an axis and has a greater extent along said axis than perpendicular to said axis. The crank chamber serves for accommodating a crankshaft.
Furthermore, at least one cylinder chamber is provided in which a piston is caused to perform a reciprocating movement by a rotation of the crankshaft.
The crank chamber has, in a first end surface, an opening through which the crankshaft can be inserted into said crank chamber. According to the invention, the inner diameter of the crank chamber narrows monotonously from the first end surface to the second end surface.
A monotonous narrowing is to be understood to mean that the inner diameter of the crank chamber only decreases or remains constant, but increases no further, on a path along the axis of said crank chamber from the first end surface to the second end surface.
It has been identified that a crank chamber shaped in this way can be manufactured particularly easily by casting the housing material around a shaping mandrel. A shaping mandrel of said type must narrow monotonously from its first end to its second end in order that it can be pulled at its first end out of the housing after the casting-around process. Crank chambers according to the previous prior art, which had the shape of a straight cylinder or had numerous undercuts, were not capable of being manufactured by means of this simple method. By means of the shaping of the crank chamber according to the invention, the housing can be of unipartite and, at the same time, very compact construction.
Here, the disadvantage was firstly accepted that, in the case of a motor or compressor with multiple cylinders, much less movement space is available in the crank chamber for at least one connecting rod of one cylinder, and thus in general the connecting rods must be of slimmer dimensions and/or the crankcase bulge close to the first end must be larger. It was identified that this disadvantage is overcompensated by the much simpler manufacture of the housing.
The crank chamber advantageously tapers in the shape of a cone or frustum from the first end surface to the second end surface. The shell of said cone or frustum is advantageously inclined with respect to its axis of symmetry by an angle of between 0.5 and 10 degrees, preferably 0.5 and 5 degrees, and very particularly preferably between 1 and 5 degrees. A shaping mandrel used for the production process can then be removed most easily after the casting-around process. The housing is advantageously cast in one piece. The housing is advantageously composed at least partially of aluminum, magnesium, titanium, of an aluminum, magnesium or titanium alloy, or of some other lightweight alloy suitable for pressure casting. The crankcase may also taper in the shape of a cone or frustum from each of the two end surfaces toward its interior, which can be manufactured for example by casting around two shaping mandrels which are subsequently pulled out in opposite directions. It is thus possible for the movement space available for the connecting rod in the vicinity of the second end surface to be enlarged. In the case of a two-cylinder compressor, it can thus be achieved, for example, that identically dimensioned connecting rods can be used for both cylinders.
The motor or compressor according to the invention has a housing according to the invention. At least two cylinder chambers for accommodating in each case one piston are provided in said housing. The pistons are driven by a crankshaft. For this purpose, one connecting rod is provided per cylinder chamber, which connecting rod is rotatably mounted by way of a first connecting-rod eye on the crankshaft and by way of a second connecting-rod eye on a piston which runs in the cylinder chamber. According to the invention, in a comparison of two connecting rods mounted along the axis of the crankshaft, the outer diameter of the connecting rod in the region of the first connecting-rod eye and/or the inner diameter of the first connecting-rod eye also narrows with the respective inner diameter of the crank chamber.
If the housing has two cylinders, for example, a first cylinder will be closer to the opening, through which the crankshaft can be inserted into the crank chamber, than the second cylinder. Then, at the location of the first connecting rod, where the inner diameter of the crank chamber is relatively large, more movement space is available for the movement of the first connecting-rod eye around the crankshaft. At the location of the second connecting rod, where the inner diameter of the crankcase is relatively small, there is accordingly less movement space available around the crankshaft for the movement of the first connecting-rod eye of the second connecting rod around the crankshaft. According to the invention, the second connecting rod is adapted to the situation.
It is self-evidently possible to use the relatively small connecting rod at both cylinders. However, with increasing thickness, a connecting rod is naturally also more stable. For the price of slightly increased outlay for the manufacture of two different parts, the power that can be transmitted by the connecting rods can thus be increased overall by using two connecting rods of different size. The exact dimensions of the connecting rods are determined on an application-specific basis by the force demands of the compressor or motor operation.
In general, the connecting rod which is closest to the drive of the compressor along the axis of the crankshaft is subjected to greater mechanical load. This also applies to the crankpin that connects the connecting rod to the crankshaft. The drive is therefore advantageously connected to that end of the crankshaft which passes through the first end surface. Then, the connecting rod which is closest to the drive has the greatest possible freedom of movement in the crank chamber and can be dimensioned to be correspondingly stronger.
In an advantageous refinement of the invention, the pistons have identical diameters and/or identical stroke travels. They particularly preferably have both identical diameters and identical stroke travels. Then, the air compression is performed uniformly; the narrowing of the crank chamber no longer has an effect on the air supply system connected downstream of the compressor. For this purpose, the compressor advantageously has only one pressure stage.
A flange is advantageously arranged on the first end surface of the crank chamber. The flange can adapt the housing to a wide variety of outputs, drives and other hardware in the engine bay of a vehicle, without the need to modify the casting mold for the housing. The crankshaft is particularly advantageously led through the flange for the purposes of connection to the output or drive.
Alternatively or in combination with this, the flange may also perform further functions. In a further advantageous refinement of the invention, the flange may be designed for the fastening of the motor or compressor in the engine bay of a vehicle. Alternatively or in combination, the flange may also be designed for the fastening of a further assembly, which is driven by means of the crankshaft, to the motor or compressor. The further assembly may, for example, be a steering assistance pump.
The cylinder chambers may be arranged entirely in the housing. The cylinder chambers may however also merely begin in the housing and continue into cylinders which are mounted as separate parts onto the housing. The cylinder barrels are wearing parts. When they have become worn, it is less expensive to merely replace a separately mounted cylinder than having to discard the housing entirely. Furthermore, weight can be saved in this way. For example, aluminum is particularly advantageous as a material for the housing because it is lightweight. By contrast, steel is more robust and is thus more suitable as a cylinder barrel. With a housing composed of aluminum and cylinders composed of steel, the specific advantages of both materials can be combined.
In the context of the invention, a method for producing a housing according to the invention has also been developed. The method is distinguished by the fact that the crank chamber is manufactured by casting the housing material around an elongate shaping mandrel which has two ends and the outer diameter of which narrows monotonously from its first end to its second end. Aluminum in particular is advantageous as a housing material.
It has been identified that the production of the crank chamber is particularly critical because it constitutes the largest cavity in the housing. By means of the shaping mandrel, stability is imparted to the cavity until the cast material has cooled and the cavity has become self-supporting. In this way, the production of a housing in one piece is dramatically simplified. After the casting-around process, the shaping mandrel is advantageously pulled at its first end out of the housing. In the case of methods other than pressure casting methods, it may however also be expedient for the shaping mandrel to be removed destructively, for example by virtue of the shaping mandrel being broken up or dissolved using a caustic agent.
The housing material should adhere as little as possible to the material of the shaping mandrel. The housing material is therefore advantageously composed of a different material than the housing material.
The shaping mandrel may in particular taper in the manner of a cone or frustum. The shell of said cone or frustum is advantageously inclined with respect to its axis of symmetry by an angle of between 5 and 30 degrees, preferably between 5 and 15 degrees.
If the shaping mandrel narrows more intensely, the crank chamber may possibly be too narrow at its second end for the movement of a connecting rod around the crankshaft. If the shaping mandrel narrows to a much lesser extent, it may be much more difficult to pull it out of the cooled housing material, and it may break when this is attempted.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.